Effective utilization of coal has attracted attention as one of the possible solutions to recent energy issues.
To convert coal to a highly value-added energy medium, advanced technologies, such as a coal gasification technology and a gas purification technology, are required.
An integrated coal gasification combined cycle system that generates electricity using gasified gas has been proposed (Patent Literature 1).
The integrated coal gasification combined cycle (IGCC) is a system that converts coal into combustible gas in a high-temperature and high-pressure gasifier and generates electricity through a combined cycle with a gas turbine and a steam turbine by using the gasified gas as fuel.
Examples of such a cycle are illustrated in FIGS. 3 and 4. FIG. 3 is an explanatory diagram showing a coal gasification power plant, and FIG. 4 is an explanatory diagram showing another coal gasification power plant.
As illustrated in FIG. 3, the coal gasification power plant 100-1 gasifies coal 101 in a gasifier 102 to obtain gasified gas 103 as synthesis gas, reduces the amount of dust in a dust removal apparatus 104, converts COS into H2S in a COS converter 105, causes a CO shift reaction to occur in a CO shift reactor 106, and recovers CO2 and reduces the amount of H2S in the gas in an H2S/CO2 recovery apparatus 107. In FIGS. 3 and 4, reference numeral 120 denotes air, 121 denotes an air separator for separating the air into nitrogen (N2) and oxygen (O2), 122 denotes a gasification air compressor, 123 denotes gasification air, 124 denotes steam, and 125 denotes an H2S/CO2 treatment system.
Synthesis gas 108 obtained through treatment by the H2S/CO2 recovery apparatus 107 is supplied to a combustor 111 in a gas turbine 110 used as power generating means and is then combusted. High-temperature and high-pressure combustion gas is thereby produced and used to drive a turbine 112. The turbine 112 is connected to a power generator 113, so that the power generator 113 generates electricity when the turbine 112 is driven. Flue gas 114 that has driven the turbine 112 has a temperature of 500 to 600° C. Therefore, it is preferable to feed the flue gas to an HRSG (Heat Recovery Steam Generator (an exhaust heat recovery boiler)) 115 in order to recover heat energy. In the HRSG 115, steam is produced by the heat energy of the flue gas, and the produced steam drives a steam turbine 116. The flue gas from which heat energy has been recovered by the HRSG 115 is fed to a denitrification apparatus (not shown) to reduce the amount of NOx in the flue gas and thereafter released into the air through a stack 117.
As described above, before CO2 is separated, the gasified gas 103 obtained through the gasification in the gasifier 102 must be subjected to the CO shift reactor 106 that generates hydrogen (H2) from carbon monoxide (CO) and steam (H2O) contained in the gasified gas 103.
The CO shift reaction is represented by the following formula (1) and performed to obtain CO2 and H2 as useful components.CO+H2O→CO2+H2  (1)
The CO shift reactor 106 converts CO contained in a large amount in the gasified gas 103 into H2. Thus, the purified gas having a composition suitable not only as turbine gas but also for the synthesis of chemical products such as ethanol and ammonia can be obtained.
In the coal gasification power plant 100-1 shown in FIG. 3, the CO shift reactor 106 including the CO shift catalyst is disposed between the COS converter 105 and the H2S/CO2 recovery apparatus 107 (on the upstream side of the H2S/CO2 recovery apparatus 107). However, the CO shift reactor 106 may be disposed on the downstream side of the H2S/CO2 recovery apparatus 107, as in another proposed coal gasification power plant 100-2 shown in FIG. 4.